[PATCH 6/7] net/9p/usbg: remove bogus context initialization in alloc_requests

[Michael Grzeschik <mgr@kernel.org>]

alloc_requests() initializes usb9pfs->in_req->context to point at the
struct f_usb9pfs instance itself. usb9pfs_queue_tx() later overwrites
this with the real struct p9_req_t pointer before every transmit, and
usb9pfs_tx_complete() clears it back to NULL after each completion, so
in_req->context only ever holds a valid p9_req_t once a request has
actually been queued.

usb9pfs_clear_tx(), however, can run at any time (mount close, gadget
disable) independent of whether a request was ever queued. If it runs
before the first usb9pfs_transmit(), it reads the leftover sentinel
value, type-confuses the struct f_usb9pfs pointer as a struct
p9_req_t, and both writes through it (req->t_err = -ECONNRESET) and
hands it to p9_client_cb(), which manipulates req->wq and req->refcount
at bogus offsets inside f_usb9pfs. This reliably corrupts memory or
panics whenever the transport is torn down before any 9p request has
been transmitted, e.g. mounting and immediately unmounting, or a cable
disconnect racing the very first request.

usb9pfs->out_req->context is set the same way but is never read by
this transport (usb9pfs_rx_complete() identifies the instance via
ep->driver_data instead), so it serves no purpose either.

Both endpoints' ->driver_data are already set to usb9pfs in
enable_endpoint(), which is what the completion handlers actually use
to recover the f_usb9pfs instance. Just drop the leftover
->context assignments; usb_ep_alloc_request()/alloc_ep_req() already
return zeroed requests, so in_req->context correctly starts out NULL.

Fixes: a3be076dc174 ("net/9p/usbg: Add new usb gadget function transport")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Michael Grzeschik <mgr@kernel.org>
---
 net/9p/trans_usbg.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/net/9p/trans_usbg.c b/net/9p/trans_usbg.c
index 9bcad638d827..544690a5c717 100644
--- a/net/9p/trans_usbg.c
+++ b/net/9p/trans_usbg.c
@@ -314,10 +314,6 @@ static int alloc_requests(struct usb_composite_dev *cdev,
 	usb9pfs->in_req->complete = usb9pfs_tx_complete;
 	usb9pfs->out_req->complete = usb9pfs_rx_complete;
 
-	/* length will be set in complete routine */
-	usb9pfs->in_req->context = usb9pfs;
-	usb9pfs->out_req->context = usb9pfs;
-
 	return 0;
 
 fail_in:

-- 
2.53.0